A 36-YEAR-old man was allegedly in a ``drug-fuelled road rage’’ when he crashed his utility into a vehicle, killing a Perth fireman and father-of-four.

Rodney Allen Beard is on trial in the West Australian Supreme Court charged with manslaughter and doing an act likely to endanger the safety of another person over the death of 51-year-old Mark Noormets in December 2012.

Beard had allegedly been involved in a road rage incident with Doug Wormall, ramming his car several times, but losing control of his ute and veering onto the wrong side of the road, striking the victim’s car.

In her opening address, prosecutor Laura Christian said two men were minding their own business when they encountered Beard on the road.

``Both would become victims of his speed-fuelled road rage,’’ she told the jury.

Ms Christian said Mr Wormall was terrified and had tried to call triple-zero during the chase, while Mr Noormets died at the scene and Beard’s leg was injured in the crash.

A blood test showed Beard had methylamphetamine and amphetamine in his system, she said.

Alan Feast, 46, testified that he had been a methylamphetamine user for 20 years and bought his drugs from the same woman as Beard.

He said Beard picked him up from a tavern the night before the crash and seemed ``off his face’’.

``He was agitated and angry,’’ Mr Feast said.

Asked how he knew Beard had been affected by drugs, Mr Feast replied: ``You just know after so long (using).’’

Mr Feast said Beard was honking his horn at road users and driving erratically at 140km/h on a highway that night.

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